Controlling fragmentation of chemically strengthened glass

ABSTRACT

A method of manufacturing a glass substrate to control the fragmentation characteristics by etching and filling trenches in the glass substrate is disclosed. An etching pattern may be determined. The etching pattern may outline where trenches will be etched into a surface of the glass substrate. The etching pattern may be configured so that the glass substrate, when fractured, has a smaller fragmentation size than chemically strengthened glass that has not been etched. A mask may be created in accordance with the etching pattern, and the mask may be applied to a surface of the glass substrate. The surface of the glass substrate may then be etched to create trenches. A filler material may be deposited into the trenches.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under contract numberHR0011-14-C-0006 awarded by Defense Advanced Research Projects Agency.The Government has certain rights to this invention.

BACKGROUND

The present disclosure relates generally to the field of materialscience, and more particularly to controlling fragmentationcharacteristics of chemically strengthened glass.

Highly stressed glass has been known to fragment into small pieces sincethe Royal Society of London studied the phenomenon known as PrinceRupert's drops in the 17^(th) and 18^(th) centuries. There are severalways to create highly stressed glass. For example, tempered glass is atype of highly stressed glass that is made using thermal treatments.Tempering the glass puts the outer surfaces into compression and theinner surfaces into tension. The glass is placed onto a roller table,taking it through a furnace that heats it well above its transitiontemperature. The glass is then rapidly cooled with forced air draftswhile the inner portion remains free to flow for a short time. The outerlayer wants to shrink as it is quickly cooled due to the glass's thermalexpansion coefficient, but is unable to due to the higher temperature ofthe inner portion. This causes the outer layer to have large residualcompressive stresses. As the interior of the glass slowly cools, it alsowants to shrink due to the material's thermal expansion coefficient.Because the outer layer has solidified into shape, the inner region isunable to shrink. This causes the inner region to have large residualtensile stresses.

Another common way to create highly stressed glass, particularly forsoda lime glass, is using chemical treatments, such as an ion exchangeprocess. A commonly used ion exchange process for soda lime glass is apotassium and sodium (K/Na) ion exchange process. Unstressed glass issubmerged in a bath containing a potassium salt, typically potassiumnitrate (KNO₃), at an elevated temperature. The sodium ions at thesurface of the glass are replaced by potassium ions from the potassiumnitrate. Because the potassium ions are roughly 30% larger than thesodium ions, the surface of the glass is put into a compressive state.The surface compression is balanced by residual internal tensilestresses. The exchange depth and the number of sodium ions replaced bypotassium ions determine the compressive layer depth and the magnitudesof the compressive and tensile stresses.

Chemically strengthened glass' properties may be modified using ionirradiation. Ion irradiation (also referred to herein as ion beamirradiation) uses particle accelerators to emit charged particles (ions)towards a material to modify the material's properties. There areseveral types of ion irradiation techniques. One type, commonly used insemiconductor fabrication and the manufacture of silicon integratedcircuits, is referred to as ion implantation.

In ion implantation, the ions may, depending on the energy at which theyare emitted towards the material, penetrate the material to a depthbefore becoming stopped in the material (“implanted”), acting as animpurity. The ions may alter the elemental composition of the target.They also may cause many chemical and physical changes in the materialby transferring their energy and momentum to the electrons and atomicnuclei of the target material. This may cause a structural change, inthat the crystal structure of the target can be damaged or evendestroyed by the energetic collision cascades. Because the ions havemasses comparable to those of the target atoms, they knock the targetatoms out of place more than electron beams do. If the ion energy issufficiently high (usually tens of MeV) to overcome the coulomb barrier,there can even be a small amount of nuclear transmutation.

SUMMARY

Embodiments of the present invention disclose a method of manufacturinga chemically strengthened glass substrate to control the fragmentationcharacteristics of the glass substrate. In an embodiment, thisdisclosure includes a method for controlling the fragmentationcharacteristics by etching and filling trenches in a glass substrate.The method may include determining an etching pattern. The etchingpattern outlines where trenches will be etched into a surface of theglass substrate. The etching pattern may be configured so that the glasssubstrate, when fractured, has a smaller fragmentation size thanunprocessed, chemically strengthened glass. A mask may be created inaccordance with the etching pattern, and the mask may be applied to asurface of the glass substrate. The surface of the glass substrate maythen be etched to create trenches. After the trenches are etched, themethod may include depositing a filler material into the trenches.

In another embodiment, this disclosure includes a method for controllingthe fragmentation characteristics of a glass substrate by masking andirradiating the substrate using an ion beam. The method may includedetermining an irradiation pattern. The irradiation pattern may outlinewhich areas of the glass substrate will be damaged by ion irradiationand which areas will be shielded from the ion beam. The irradiationpattern may be configured so that the glass substrate, when fractured,has a smaller fragmentation size than chemically strengthened glass thathas not been irradiated. A mask may be created in accordance with theirradiation pattern, and the mask may be applied to a surface of theglass substrate. An ion beam may be raster-scanned across the surface ofthe glass substrate to generate regions of damaged glass.

In another embodiment, this disclosure includes a method for controllingthe fragmentation characteristics of a glass substrate by selectivelydepositing a metal on top of the substrate using a photolithographyprocess. A deposit pattern may be determined. The deposit pattern mayoutline which areas of the surface of the glass substrate will have ametal deposited on them. The deposit pattern may be configured so thatthe glass substrate, when fractured, has a smaller fragmentation sizethan chemically strengthened glass without metals deposited on top. Alayer of metal may be deposited on a surface of the glass substrate. Amask may be created in accordance with the deposit pattern, and the maskmay be applied on top of the metal layer. The metal may then bepatterned according to the deposit pattern using a photolithographyprocess.

The above summary is not intended to describe each illustratedembodiment or every implementation of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included in the present application are incorporated into,and form part of, the specification. They illustrate embodiments of thepresent invention and, along with the description, serve to explain theprinciples of the invention. The drawings are only illustrative oftypical embodiments of the invention and do not limit the invention.

FIG. 1 illustrates a flowchart of an example method of manufacturing achemically strengthened glass substrate to control the fragmentationcharacteristics of the glass substrate by etching trenches into theglass substrate and then filling the trenches, in accordance withembodiments of the present disclosure.

FIGS. 2A-C illustrate chemically strengthened glass being etchedaccording to a pattern to control the fragmentation characteristics ofthe glass, in accordance with embodiments of the present disclosure.

FIGS. 3A-C illustrate the trenches of etched chemically strengthenedglass being filled with a metal to control the fragmentationcharacteristics of the glass, in accordance with embodiments of thepresent disclosure.

FIGS. 4A-D illustrate the trenches of etched chemically strengthenedglass being layered with a chemically reactive combination of materialsto control the fragmentation characteristics of the glass, in accordancewith embodiments of the present disclosure.

FIG. 5 illustrates a flowchart of an example method of manufacturing achemically strengthened glass substrate to control the fragmentationcharacteristics of the glass substrate by masking and irradiating theglass substrate with an ion beam, in accordance with embodiments of thepresent disclosure.

FIGS. 6A-C illustrate the process of masking and irradiating a planarsheet of chemically strengthened glass with an ion beam to control thefragmentation characteristics of the glass, in accordance withembodiments of the present disclosure.

FIG. 7 illustrates a flowchart of an example method of manufacturing achemically strengthened glass substrate to control the fragmentationcharacteristics of the glass substrate by depositing a metal layer ontop of the glass substrate using a photolithography process to modifythe stress field of the glass, in accordance with embodiments of thepresent disclosure.

FIGS. 8A-C illustrate the process of depositing a metal layer on top ofa planar sheet of chemically strengthened glass using photolithographyto control the fragmentation characteristics of the glass, in accordancewith embodiments of the present disclosure.

FIGS. 9A-B illustrate the process of bonding a patterned glass substrateto a chemically strengthened glass substrate to control thefragmentation characteristics of the glass substrate, in accordance withembodiments of the present disclosure.

While the embodiments described herein are amenable to variousmodifications and alternative forms, specifics thereof have been shownby way of example in the drawings and will be described in detail. Itshould be understood, however, that the particular embodiments describedare not to be taken in a limiting sense. On the contrary, the intentionis to cover all modifications, equivalents, and alternatives fallingwithin the spirit and scope of the invention.

DETAILED DESCRIPTION

The present disclosure relates generally to the field of materialscience, and more particularly to controlling fragmentationcharacteristics of chemically strengthened glass. While the presentdisclosure is not necessarily limited to such applications, variousaspects of the disclosure may be appreciated through a discussion ofvarious examples using this context.

The basic mechanism by which fragmentation occurs has only recently beenunderstood using the framework of fracture mechanics. The fragmentationphenomenon relies on the glass having an interior region in a highlytensile state contained within an exterior that is compressivelystressed. If a flaw is introduced into the tensile region of the glass,the glass experiences a large mode I crack driving force due to therelease of strain energy from the stressed region. The high strainenergy release rate causes a tensile crack to advance through the glassat speeds approaching the speed of sound. As the crack propagatesthrough the glass, it bifurcates due to the interaction between thestress field in front of the crack and stress waves. The more often thecrack bifurcates, the smaller the fragments will be.

The crack propagation may have two components. The crack may tunnelthrough the bulk of the material, and the crack may travel towards thesurface of the material. For chemically strengthened glass, the crackfront tunneling through the bulk of the material experiences a high, andmostly constant, crack driving force through the tensile region of thesubstrate. This allows it to propagate at a relatively steady velocity,close to the speed of sound, and allows it to branch and create anetwork of cracks in the tensile region of the substrate.

The crack front moving towards the surface of the substrate, however,experiences a varying stress field due to the transition from a tensilestress region near the center of the substrate to a compressive stressregion near the surface of the substrate. The large residual compressivestresses in the region near the surface of the substrate cause the crackdriving force to decrease as the crack approaches the surface, and thecrack's propagation may be slowed or halted in this direction. The rateat which the crack bifurcates as it approaches the surface may alsodecrease. Due to this phenomenon, referred to herein as “crazing,” itbecomes difficult to decrease the size of the glass fragments byincreasing the residual tensile stresses through a prolonged ionexchange process because extending the ion exchange process alsoincreases the residual compressive stresses and the size of thecompressive stress region.

As used herein, the “fragmentation characteristics” of a glass substratedescribe how the glass fragments when fractured. Fragmentationcharacteristic include, e.g., the size, shape, and distribution offragments of glass during and after fracturing. The “fragmentation size”is a fragmentation characteristic pertaining to the width of thefragments of the glass substrate upon fracturing. The fragmentation sizemay be the average of the largest linear widths of the fragments createdby the fracturing of the glass substrate. For example, a rectangularfragment of glass with a first edge being 250 microns wide, and a secondedge being 100 microns wide will have a fragment width of roughly 269microns because that is the largest distance across a surface of theglass substrate, in this case from corner to opposite corner.Fragmentation characteristics of chemically strengthened glass can becontrolled by altering the glass's stress field. As discussed herein,various techniques are disclosed to produce an inhomogeneous stressfield in the chemically strengthened glass to control the fragmentationcharacteristics of the glass. By altering the stress field within theglass, the frequency of the crack bifurcation may be increased to causethe glass to fragment into smaller pieces.

A “stress field” describes the magnitude and type of stress (e.g.,compressive, tensile) throughout a body, or throughout a region of abody. An “inhomogeneous stress field” is a stress field where thestresses within a material are not uniform. For example, a chemicallystrengthened glass substrate may have surfaces in compression while thebulk of the material is in tension. The stress field for the chemicallystrengthened glass substrate may be considered inhomogeneous because thestresses throughout the glass substrate are not the same.

Residual stresses are stresses that remain in a solid material after theoriginal cause of the stresses has been removed. Residual stresses maybe compressive or tensile. A material has a “residual compressivestress” if a region of the material continues to be in compression afterthe stressor is removed. A material has a “residual tensile stress” if aregion of the material continues to be in tension after the stressor isremoved. Residual stresses may affect the properties of the material,and may be desirable or undesirable. For example, residual compressivestresses tend to increase the strength of a material, while residualtensile stresses tend to increase the crack driving force in a materialduring fracture. Some solid materials, such as chemically strengthenedglass, have both residual compressive and tensile stresses.

FIG. 1 illustrates a flowchart of an example method 100 of manufacturinga chemically strengthened glass substrate to control the fragmentationcharacteristics of the glass substrate by etching trenches into theglass substrate and then filling the trenches, in accordance withembodiments of the present disclosure. In some embodiments, the method100 may be performed on a glass substrate prior to the glass substratebeing chemically strengthened using an ion exchange process. The method100 may begin at operation 102, wherein an etching pattern and a fillermaterial are determined. The etching pattern defines the locations oftrenches and/or holes in the glass substrate. The etching pattern may beconfigured in conjunction with the filler material to control thefragmentation characteristics of the chemically strengthened glass. Forexample, the etching pattern and filler material may be chosen tominimize the fragmentation size of the glass substrate. Thefragmentation characteristics of the glass are controlled by modifyingthe stress field within the glass substrate.

The filler material may be chosen in conjunction with the etchingpattern to alter the stress field within the glass substrate. The fillermaterial may be any material that can be deposited into the trenches,such as metals, ceramics, other types of glass, or chemically reactivematerials. The etching pattern and filler material may be chosentogether because some etching patterns will be particularly effectivewhen paired with complementary filler materials. For example, theetching pattern that is effective when depositing a metal in thetrenches may not work as well when chemically reactive materials aredeposited in the trenches.

The etching pattern may be determined according to the intended use ofthe glass. In some embodiments, the etching pattern may be chosen tolimit the crazing effects by reducing the thickness of the compressivestress region at specific places in the glass substrate. In theseembodiments, the etching pattern may cause most of the surface of theglass to be etched to reduce the thickness of compressive stress region.Only smaller areas of the glass, such as where the high strength createdby the compressive stress region is needed to, e.g., support a chip orsemiconductor, may be masked. The rest of the glass may be etched,thereby causing it to fracture into smaller fragments. In someembodiments, such as where a planar glass substrate will be supportedalong its perimeter, as in a car window, the etching pattern may involvemasking the edges of the glass and etching the rest of the planarsurface. This may preserve the higher strength along the edges of theglass, while still causing the central region of the glass to fragmentinto smaller pieces when fractured.

In embodiments where a metal filler is used, several etching patternsmay reduce the fragmentation size of the glass. In some embodiments, anetching pattern which may reduce the fragmentation size of the glass mayinclude parallel trenches across the surface of the glass substrate. Byadjusting the spacing between, and the thickness of, the trenches, aswell as the filler metal used, the fragment size of the glass substratemay be controlled. For example, reducing the spacing between thetrenches may reduce the fragmentation size. For some metals, there maybe a critical spacing length, which is the trench spacing that resultsin the smallest fragmentation size for a glass substrate. For example, aglass substrate with trenches 20 micrometers apart may have the smallestfragmentation size when the trenches are filled with aluminum. Trenchspacing that is greater than or less than the critical spacing lengthmay result in larger fragmentation size than trench spacing at thecritical spacing length.

Likewise, for some metal fillers, glass with narrower (and morefrequent) trenches may have a reduced fragmentation size when comparedto glass with wider trenches. As with the trench spacing, there may be acritical trench width, which is the trench width that results in thesmallest fragmentation size for a glass substrate. For example, glasssubstrates with trench widths of 15 micrometers may have the smallestfragmentation size when the filler material is aluminum. Glasssubstrates with wider or narrower trench widths may have a largerfragmentation size than glass with trench widths at the critical trenchwidth.

In some embodiments, the etching pattern may include etching trenches inthe shape of disconnected features into the surface of the glasssubstrate. The disconnected features may be open features (such aszig-zag or c-shaped patterns) or closed features (such as a rectangle ora star). The features may be considered disconnected because thetrenches that define the features do not cross or touch neighboringfeatures' trenches. Not only can the trenches reduce the compressivestresses as previously discussed, the use of a disconnected feature,such as a star, may help to increase the bifurcation of the crack.

For example, assume that a five-point star is etched into the surface ofa glass substrate. As a crack propagates through the substrate, it mayintersect the star. The crack may then follow the edges of the star,cracking outward every time it reaches a point in the star, which mayact like a stress concentration point. Accordingly, by changing thenumber of points in the star and the size of the star, the frequency ofthe crack bifurcation may be controlled. Decreasing the size of the staror increasing the number of points in the star may reduce thefragmentation size of the glass substrate.

In some embodiments, disconnected features may be etched into thesurface in order to control the fragmentation shape of the glass. Shapeslike rectangles or stars may be etched into the glass surface so that,upon fracturing, the fragments are shaped like the features, e.g., likea rectangle or star. Controlling the shape of the fragmentation may makeit easier to separate the fractured glass from its environment. Forexample, chemically strengthened glass may be used in a pipe to holdback the flow of a fluid, such as seawater at a water desalinationplant, until the pipe is connected to the desalination equipment and theplant is ready to being operations. At that point, the glass may beintentionally broken (e.g., by increasing the water pressure in thepipe). The glass may then be filtered out of the water, and bycontrolling the shape of the fragments of glass, it may be easier orcheaper to filter the majority of the glass out of the water.

In some embodiments, the etching pattern may be chosen to limit thecrazing effects by reducing the magnitude of the compressive stresses atthe surface of the glass. For example, a metal may be deposited into thetrenches at a high temperature, allowing the metal to bond with theglass substrate at the boundaries between the metal and glass (e.g., atthe trench walls and along the bottom of the trench). Because thetrenches were etched into the compressive region of the chemicallystrengthened glass, the trench walls may have residual compressivestresses when the metal is deposited into the trenches. The metal maythen be allowed to cool, which may cause the metal to contract. As themetal contracts, it may pull on the walls of the trenches in a directiontowards the contracting metal (e.g., towards the center of the trench).This may create tensile stresses along the trench walls. The tensilestresses may counter and reduce the residual compressive stresses thatoriginally resided in the trench walls. By decreasing the magnitude ofthe compressive stresses, the crazing effects responsible for largerfragmentation sizes when the glass fractures may be reduced.

In some embodiments, the trenches in the glass may be filled with acomposition of two or more chemically reactive materials. In someembodiments, the chemically reactive compound may be layered inside thetrenches. For example, alternating layers of elemental aluminum andnickel may be deposited in the trenches. A reaction between the aluminumand nickel may be initiated by heating the glass. In embodiments, thereaction may be initiated by inserting a filament into the trenches withthe aluminum and nickel, and then heating the filament by running acurrent through it.

The thermal pulse created by igniting the chemically reactive compoundsmay be used to change the stress field within the glass. When thechemically reactive compound is ignited, it may produce heat and/orchange volume. The reaction may locally heat the glass, relieving ordecreasing the residual stresses in the heated portion of the glass.This may be particularly advantageous in the compressively stressedlayers of the glass, as residual compressive stresses can inhibitfracturing of the glass, causing fragments to be larger than desired. Bycombining the chemically reactive material with an appropriate etchingpattern, the compressive stresses in specific parts of the glass may berelieved and the fragmentation characteristics of the glass may becontrolled.

In some embodiments, the volumetric change that some chemically reactivematerials undergo during the chemical reaction may be used to alter thestress field inside the glass. For example, the products of the reactionmay have a smaller volume than the reactants. Accordingly, when thereactants, which are bound or fused with the walls of the trenches,undergo the chemical reaction, the volume of the material inside thetrenches may decrease. This, in turn, may cause the products of thereaction to pull on the walls of the trenches, creating tensile stressesat the trench walls. The tensile stresses may counter and reduce theresidual compressive stresses that originally resided in the trenchwalls.

Because the magnitude of the compressive tensile stresses may bereduced, the crazing effects may be reduced. This may allow a crack topropagate faster and further in the compressive stress region, which inturn may increase the rate of bifurcation of the crack, leading to asmaller fragmentation size. This may be a particularly advantageousmethod because the change in the volume of the filler materials that mayresult from a chemical reaction may be upwards of 10% or more, while thechange in volume from increasing the temperature of a metal may becloser to 1% or 2%. Accordingly, the use of chemically reactivematerials may better relieve the compressive stresses than simplydepositing a metal in the trenches does.

In some embodiments, the rapid expansion of gasses released during somechemical reactions may be used to alter the stress field inside theglass. As the gasses expand, they create a pressure on the walls of thetrenches. This pressure may impart additional residual stresses on theglass. By carefully controlling where the pressure will impart residualstresses through selectively etching the surface of the glass substrate,the stress field within the glass may be modified. This may beparticularly advantageous when larger fragmentation sizes are desiredbecause the expanding gasses may increase the magnitude of the residualcompressive stresses near the surface of the glass. In some embodiments,the expansion of the gasses may be strong enough to fracture the glass,and igniting the chemically reactive compounds may be done tointentionally initiate fragmentation.

In some embodiments, it may be advantageous to increase thefragmentation size of a chemically strengthened glass substrate. Inthese cases, the trenches may be etched such that they form a cross ormesh-like pattern. The width of the trenches, spacing between paralleltrenches, angles of intersection of trenches, and area of the gapscreated by the mesh pattern may all be considered when determining anetching pattern. A mesh-like etching pattern allows crack propagation tobe directed towards metal at a roughly orthogonal angle, which can beused to stop the crack from continuing on or bifurcating further.Accordingly, the size of the fragments of glass can be made larger thannormally produced by chemically strengthened glass with the sameresidual tensile stresses.

Parallel trenches may be particularly useful in controlling thedistribution of fragmentation sizes. Unlike with disconnected features,which may be difficult to uniformly pattern across the surface of theglass, parallel lines can be uniformly distributed across the surface ofthe glass substrate. This may change the distribution of thefragmentation sizes such that a higher percentage of glass fragments areat or near a desired size, while the range and standard deviation of thesize of individual glass fragments may be smaller.

In some embodiments, the trenches may be filled with a thermallymismatched filler material to increase the fragmentation size of theglass. The filler material may have a larger thermal expansioncoefficient than the glass so that it expands and contracts withchanging temperatures at an increased rate, and to a larger extent, thanthe glass itself. The material may also have a higher Young's modulus,meaning that the material is more rigid than the glass. As thetemperature increases, the filler material expands. As the fillermaterial expands (and in turn resists the expansion of the glass), itmay create a pressure along the walls of the trenches. This pressure maychange the stress field within the glass substrate, particularly at ornear the trench walls, by increasing the residual compressive stresses.Accordingly, the fragmentation size of the glass substrate may beincreased. In some embodiments, the expansion of the filler material maybe large enough to cause the glass substrate to fracture. This may beintentionally selected to initiate fragmentation of the glass substratewhen the glass reaches a certain temperature. For example, a glasssubstrate with a current-carrying wire running through it may befractured when the glass reaches a specific temperature. This may beused to, e.g., trigger an alarm.

After determining the etching pattern and filler material at operation102, a mask may be created according to the etching pattern at operation104. The material that the mask is made out of may depend on the etchingtechnique employed. For example, if the glass will be etched bysubmersion in a concentration of buffered hydrofluoric acid, the maskmay be made out of a material resistant to corrosion in hydrofluoricacid.

After creating a mask at operation 104, the mask may be applied to asurface of the glass substrate, and the portions of the substrate notprotected by the mask may be etched at operation 106. Any method ofetching glass may be used. For example, the glass may be etched using aliquid (“wet”) etching technique, such as by submerging the masked glassin a concentration of hydrofluoric acid. Glass may also be etched usinga plasma (“dry”) etching process. Dry etching processes that may beemployed include ion milling (also known as sputter etching),reactive-ion etching (RIE), and deep reactive-ion etching (DRIE). Insome embodiments, the glass may be etched using a mechanical finishingprocess, such as by sandblasting or milling.

After applying the mask and etching trenches into the chemicallystrengthened glass at operation 106, the trenches may be filled with thefiller material at operation 108. The trenches may be filled using anytechnique for depositing the filler material into the trenches. Forexample, a thin-film deposition process, such as an evaporation process,where the filler material is evaporated and then condenses back to asolid state, may be used. After the trenches have been filled atoperation 108, the method 100 may end.

FIGS. 2A-C illustrate chemically strengthened glass 200 being etchedaccording to an etching pattern to control the fragmentationcharacteristics of the glass, in accordance with embodiments of thepresent disclosure. The chemically strengthened glass 200 may be madeusing any chemical strengthening process. For example, the chemicallystrengthened glass may be made using an ion exchange process, such as aK/Na ion exchange process that replaces sodium ions in the surface ofthe glass with larger potassium ions when soda lime glass is placed inpotassium nitrate (KNO₃). In some embodiments, the ion exchange processused to strengthen the glass 200 may involve replacing the sodium ionswith some other ions, such as rubidium ions.

As shown in FIG. 2A, a mask 202 may be created to pattern the glass 200to create an inhomogeneous stress field inside the glass. The pattern ofthe mask 202 may be chosen to create an inhomogeneous stress field thatresults in the desired fragmentation characteristics of the glass. Themask 202 may be applied to the surface of the glass 200. As shown inFIG. 2B, the unmasked portion of the glass may then be etched using anyglass etching process, such as those examples given in reference toFIG. 1. The etching process may create a plurality of trenches or holes204. After the glass 200 has been etched and a plurality of trenches 204have been created, the mask 202 may be removed from the glass, leavingbehind an etched glass surface as shown in FIG. 2C.

FIGS. 3A-C illustrate the trenches 302 of etched, chemicallystrengthened glass 300 being filled with a metal to control thefragmentation characteristics of the glass, in accordance withembodiments of the present disclosure. The chemically strengthened glass300 may be made using any chemical strengthening process. For example,the chemically strengthened glass may be made using an ion exchangeprocess, such as a K/Na ion exchange process that replaces sodium ionsin the surface of the glass with larger potassium ions when soda limeglass is placed in potassium nitrate (KNO₃). In some embodiments, theion exchange process used to strengthen the glass 300 may involvereplacing the sodium ions with some other ions, such as rubidium ions.

As shown in FIG. 3A, the etched glass 300 may have a plurality oftrenches or holes 302 on a first surface. A metal 304 may then bedeposited on the first surface, as shown in FIG. 3B. The metal may bedeposited using any technique for depositing a metal on a substrate. Theprocess of depositing the metal 304 of the glass 300 may leave metal notonly in the plurality of trenches 302, but also on top of the firstsurface of the glass. The first surface of the glass 300 may be polishedto remove extraneous metal, leaving metal only in the trenches 302 ofthe glass as shown in FIG. 3C.

FIGS. 4A-D illustrate the trenches 402 of etched, chemicallystrengthened glass 400 being layered with a chemically reactivecombination of materials to control the fragmentation characteristics ofthe glass, in accordance with embodiments of the present disclosure. Thechemically strengthened glass 400 may be made using any chemicalstrengthening process. For example, the chemically strengthened glassmay be made using an ion exchange process, such as a K/Na ion exchangeprocess that replaces sodium ions in the surface of the glass withlarger potassium ions when soda lime glass is placed in potassiumnitrate (KNO₃). In some embodiments, the ion exchange process used tostrengthen the glass 400 may involve replacing the sodium ions with someother ions, such as rubidium ions.

As shown in FIG. 4A, the etched glass may have a plurality of trenchesor holes 402 on a first surface. A first reactive material 404 (e.g.,aluminum) may be deposited in the trenches 402 of the glass 400 as shownin FIG. 4B. After a layer of the first reactive material 404 has beendeposited in the trenches 402, a layer of a second reactive material 406(e.g., nickel) may be deposited in the trenches of the glass 400 on topof the lay of the first reactive material. A diagram showing one layerof each material is shown in FIG. 4C. Another layer of the firstreactive material 404 may then be deposited on top of the layer of thesecond reactive material 406. The process of layering the trenches withalternating reactive materials may continue until the trenches are full,as shown in FIG. 4D.

In some embodiments, such as the one shown in FIGS. 4A-D, the chemicallyreactive combination may involve layering two different materials (e.g.,aluminum and nickel). In other embodiments, additional layers may benecessary or preferred. For example, a layer of a third material, suchas an oxide, may sit on top of the layers of the two reactive materialsto enhance the chemical reaction. As another example, a catalyst layermay be deposited in the trenches to increase the rate at which thereactants undergo the chemical reaction.

FIG. 5 illustrates a flowchart of an example method 500 of manufacturinga chemically strengthened glass substrate to control the fragmentationcharacteristics of the glass substrate by masking and irradiating theglass substrate with an ion beam, in accordance with embodiments of thepresent disclosure. Ion beam irradiation works by depositing chargedparticles (ions) in a substrate. At a high enough incident energy, theions are able to penetrate the substrate and, depending on the ions'energy, break bonds between atoms in the substrate. At lower incidentenergies, an ion beam may not be able to penetrate all the way throughthe substrate. Instead, the ions may be implanted in the substrate,creating impurities. Because the ion beam may fan out in a cone-likeshape, the ion beam may have a central incidence axis, which is the axisthat runs from the center of the ion emitter to the center of the areaon the glass substrate that is hit by the ion beam. In some embodiments,the method 500 may be performed on a glass substrate prior to the glasssubstrate being chemically strengthened using an ion exchange process.The method 500 may begin at operation 502, wherein an irradiationpattern may be determined. The irradiation pattern may establish whichparts of the glass substrate will be subjected to ion irradiation, andwhich parts of the glass substrate will be protected (or masked) fromthe ion irradiation.

In some embodiments, the irradiation pattern may be chosen to createsmall pockets of damaged glass throughout the glass substrate bybreaking bonds in the glass or by implanting ions in the glass. Anexample of using ion irradiation to create pockets of damaged glass isshown in FIG. 6A-C. The pockets of damaged glass may be made anywhere inthe glass, such as in either the compressive region or the tensileregion.

For example, the irradiation pattern may be chosen to break bonds andweaken the glass near the surface, in the compressive region. This mayreduce the fragmentation size of the glass because the compressiveregion may be weaker (fewer bonds between atoms) and, therefore, moresusceptible to fracturing. In some embodiments, the pockets of damagedglass may be focused at the transitional region between the tensilestress region and the compressive stress region to assist the crack inpropagating towards the surface of the substrate.

In some embodiments, the irradiation pattern may be chosen to create oneor more paths of damaged glass that run through the glass substrate. Insome embodiments, the paths of damaged glass may tunnel through the bulkof the material. This may provide a path through which the crack maymore easily propagate. In some embodiments, the damaged region may runfrom at or near the surface of the glass (in the compressive region) toat or near the center of the glass (in the tensile region). This mayprovide a path through which cracks may more easily propagate towardsthe surface of the glass, helping to overcome the crazing effects of thecompressive region. The ion beam energy may be modulated to adjust thedepth of the damage or implantation to create the path from the tensileregion to the compressive region.

For example, in some embodiments, the ion beam may be raster-scannedacross the masked glass surface to create a damaged region of glass at afirst depth. The ion beam's energy may then be adjusted to change thedepth at which the damage is done to the glass, and subsequently, theion beam may be raster-scanned across the masked glass surface again.This process may be repeated until the ion beam has created a path ofdamaged glass that runs from a point in the tensile region of thesubstrate to a point in the compressive region of the substrate.

The irradiation pattern may be determined according to the intended useof the glass. In some embodiments, the irradiation pattern may be chosento limit the crazing effects by damaging the compressive stress regionat specific places on the glass substrate. In these embodiments, theirradiation pattern may cause most of the surface of the glass to beirradiated to damage the compressive region of the glass substrateacross most of the surface. Only smaller areas of the glass, such aswhere the high strength created by the compressive stress region isneeded to, e.g., support a chip or semiconductor, may be masked. Therest of the glass may be irradiated, thereby causing it to fracture intosmaller fragments.

In some embodiments, such as where a planar glass substrate will besupported along its perimeter, as in a car window, the irradiationpattern may involve masking the edges of the glass and irradiating therest of the planar surface. This may preserve the higher strength alongthe edges of the glass, while still causing the central region of theglass to fragment into smaller pieces when fractured.

Different irradiation patterns may be used to reduce the fragmentationsize of the glass. In some embodiments, parallel paths of damaged glassmay be created by raster-scanning the ion beam across the surface of theglass substrate. By adjusting the spacing and thickness of the damagedpaths, the fragment size of the glass substrate may be controlled. Forexample, reducing the spacing between the damaged paths may reduce thefragmentation size.

Parallel damage paths may be particularly useful in controlling thedistribution of fragmentation sizes. Unlike with disconnected features,which may be difficult to uniformly pattern throughout the glasssubstrate, parallel lines can be uniformly distributed across throughouta section of the glass substrate more easily. This may change thedistribution of the fragmentation sizes such that a higher percentage ofglass fragments are at or near a desired size, while the range andstandard deviation of the size of individual glass fragments may besmaller.

There may be a critical spacing length for the damaged paths in theglass substrate. Damaged path spacing that is greater than or less thanthe critical spacing may result in a larger fragmentation size thandamaged path spacing at the critical spacing length. Likewise, glasswith narrower (and more frequent) damaged path widths may have a reducedfragmentation size when compared to glass with wider path widths. Aswith the path spacing, there may be a critical path width. Glass withwider or narrower damaged path widths may have a larger fragmentationsize than glass with damage path widths at the critical path width.

In some embodiments, the irradiation pattern may include creatingdamaged glass regions in the form of disconnected features. Thedisconnected features may be open features (such as zig-zag or c-shapedpatterns) or closed features (such as a rectangle or a star). Thefeatures may be considered disconnected because the paths of damagedglass that define the features do not cross or touch neighboringfeatures' paths of damaged glass. Not only can the damaged regionsreduce the compressive stresses as discussed herein, the use of adisconnected feature, such as a star, may help to increase thebifurcation of the crack.

For example, assume that a glass substrate is irradiated so as to createa damaged region in the shape of a five-point star. As a crackpropagates through the substrate, it may intersect the star. The crackmay then follow the edges of the star, cracking outward every time itreaches a point in the star, which may act like a stress concentrationpoint. Accordingly, by changing the number of points in the star and thesize of the star, the frequency of the crack bifurcation may becontrolled. Decreasing the size of the star or increasing the number ofpoints in the star may reduce the fragmentation size of the glasssubstrate.

In some embodiments, a glass substrate may be irradiated to createdisconnected features in the substrate in order to control thefragmentation shape of the glass. Damaged regions of glass in the shapesof rectangles or stars may be generated in the glass substrate using anion beam so that, upon fracturing, the fragments are shaped like thefeatures, e.g., like a rectangle or star. Controlling the shape of thefragmentation may make it easier to separate the fractured glass fromits environment. For example, chemically strengthened glass may be usedin a pipe to hold back the flow of a fluid, such as seawater at a waterdesalination plant, until the pipe is connected to the desalinationequipment and the plant is ready to being operations. At that point, theglass may be intentionally broken (e.g., by increasing the waterpressure in the pipe). The glass may then be filtered out of the water,and by controlling the shape of the fragments of glass, it may be easieror cheaper to filter the majority of the glass out of the water.

After determining an irradiation pattern at operation 502, a mask may becreated according to the irradiation pattern at operation 504. The maskmay be made out of any material capable of protecting the glasssubstrate from the ion beam. The mask material may depend on the energylevels and types of ions used by the ion beam because some maskingmaterials may not be able to shield the glass from ion beams with anenergy level about a threshold. After creating a mask at operation 504,the mask may be applied to a surface of the glass substrate at operation506. At operation 508, the glass substrate may be irradiated with an ionbeam.

In some embodiments, the ion beam may irradiate the glass surface withhydrogen ions. In some embodiments, the ion beam may irradiate the glasssubstrate with heavier ions, such as gallium ions. In some embodiments,the glass substrate may be irradiated with a combination of differentions.

In some embodiments, the glass substrate (or the ion beam) may be tiltedto create complex patterns of damaged glass within the substrate. Theglass substrate may have more than one surface masked, or the masks maybe changed during the irradiation process. For example, an ion beam maybe raster-scanned across a masked surface of a glass substrate. The maskmay then be removed from the surface, and a new mask may be applied tothe same surface. The glass substrate may then be tilted so that the ionbeam approaches the masked surface from a different angle, and the ionbeam may again be raster-scanned across the masked surface. This processmay be repeated to create complex paths and regions of damage within theglass substrate.

As another example, a piece of chemically strengthened glass may bemasked on a first surface and a second surface, wherein the two surfacesmeet at a substantially orthogonal angle (i.e., between 80 and 100degree). The ion beam may then be raster-scanned across the firstsurface, creating areas of damaged glass within the substrate. The glasssubstrate may then be tilted 90 degrees to expose the second surface tothe ion beam. The ion beam may then be raster-scanned across the secondsurface. This may allow more complex damage patterns, such as cross or“T” shaped patterns, to be created in the glass substrate. After theglass substrate has been irradiated, the method 500 may end.

In some embodiments, ions may be implanted in the glass substrate usingan ion beam irradiation process that does not require a mask. Forexample, the ion beam may be raster-scanned over a section of the glasssubstrate, e.g., over a square or a rectangular shaped section of theglass surface. The ion beam may then be “blanked,” or turned off, andthe glass (or the beam) may then be mechanically translated in adirection to change the area of the glass that is targeted by the ionbeam. The ion beam may then be activated again when the ion beam isdirected towards the next part of the glass to be irradiated. Thisprocess may be repeated as necessary to damage the glass substrate inaccordance with the irradiation pattern.

FIGS. 6A-C illustrate the process of masking and irradiating a planarsheet of chemically strengthened glass 600 with an ion beam to controlthe fragmentation characteristics of the glass, in accordance withembodiments of the present disclosure. The chemically strengthened glass600 may be made using any chemical strengthening process. For example,the chemically strengthened glass may be made using an ion exchangeprocess, such as a K/Na ion exchange process that replaces sodium ionsin the surface of the glass with larger potassium ions when soda limeglass is placed in potassium nitrate (KNO₃). In some embodiments, theion exchange process used to strengthen the glass 600 may involvereplacing the sodium ions with some other ions, such as rubidium ions.

As shown in FIG. 6A, a mask 602 may be created to pattern the glass 600to create an inhomogeneous stress field inside the glass. The pattern ofthe mask 602 may be chosen to create an inhomogeneous stress field thatresults in the desired fragmentation characteristics of the glass. Themask 602 may be applied to the surface of the glass 600. The surface ofthe glass may then be irradiated by an ion beam 604. The ion beam mayuse, e.g., hydrogen ions.

As shown in FIG. 6B, the ion beam irradiation 604 may penetrate theglass substrate 600 and create pockets of damaged glass 606 within theglass. The pockets of damaged glass 606 may be areas where bonds betweenthe atoms have been broken. In some embodiments, the pockets of damagedglass 606 may be areas where ions from the ion beam 604, such ashydrogen ions, have been implanted in the glass substrate 600. After theion beam irradiation has been performed on the glass 600, the mask 602may be removed, leaving behind a damaged glass substrate as shown inFIG. 6C.

While shown at a particular depth and size in FIG. 6C, other depths andsizes consistent with this disclosure are contemplated, as discussed inreference to FIG. 5. Additionally, the area of damaged glass may notalways have a rectangular cross-section, as shown in FIG. 6C, and thepresent disclosure should not be limited to damaged glass with arectangular cross-section. The damage pattern shown in FIG. 6C is usedfor illustrative purposes only, and any other damage pattern that may becreated by ion beams consistent with the application is contemplated.For example, in some embodiments, the cross section of the area ofdamaged glass may be circular. In some embodiments, the cross section ofthe area of damaged glass may be in the shape of a tear-drop.

FIG. 7 illustrates a flowchart of an example method 700 of manufacturinga chemically strengthened glass substrate to control the fragmentationcharacteristics of the glass substrate by depositing a metal layer ontop of the glass substrate using a photolithography process to modifythe stress field of the glass, in accordance with embodiments of thepresent disclosure. In some embodiments, the method 700 may be performedon a glass substrate prior to the glass substrate being chemicallystrengthened using an ion exchange process. The method 700 may begin atoperation 702, wherein a deposit pattern may be determined. The depositpattern establishes which parts of the glass substrate will have a layerof metal deposited on top, and which parts of the metal layer will beetched away.

Layers of metal deposited on the surface of a glass substrate change thestress field within the substrate, particularly at and near the surfacewhere the metal is deposited. This may be caused by, e.g., the weight ofthe metal and the bonding between the metal and the glass substrate. Byselectively depositing metal according to pattern, the stress field ofthe glass may be modified to change the fragmentation characteristics ofthe glass. Because the metal is deposited on the surface, where residualcompressive stresses are located in chemically strengthened glass,selectively depositing the metal layer may be particularly useful inminimizing the crazing effects of the compressive stress region. Thedeposited metal may also provide a path, predominantly at the edges ofthe metal-glass bond, for cracks to follow.

In embodiments, several deposit patterns may be used to control thefragmentation size of the glass. In some embodiments, parallel lines ofmetal may be deposited across the surface of the glass substrate. Byadjusting the spacing and thickness of the lines, the fragment size ofthe glass substrate may be controlled. For example, reducing the spacingbetween the lines may reduce the fragmentation size. For some metals,there may be a critical spacing length, which is the spacing betweendeposited lines of metal that results in the smallest fragmentationsize. Line spacing that is greater than or less than the criticalspacing may result in larger fragmentation size than line spacing at thecritical spacing length. Likewise, glass with narrower (and morefrequent) lines may have a reduced fragmentation size when compared toglass with wider lines. As with the line spacing, there may be acritical line width. Glass with wider or narrower deposit line widthsmay have a larger fragmentation size than glass with line widths at thecritical line width.

Parallel lines of deposited metal may be particularly useful incontrolling the distribution of fragmentation sizes. Unlike withdisconnected features, which may be difficult to uniformly patternacross the surface of the glass, parallel lines can be uniformlydistributed across the surface of the glass substrate. This may changethe distribution of the fragmentation sizes such that a higherpercentage of glass fragments are at or near a desired size, while therange and standard deviation of the size of individual glass fragmentsmay be smaller.

In some embodiments, the deposit pattern may include depositing lines toform disconnected features on the surface of the glass substrate. Thedisconnected features may be open features (such as zig-zag or c-shapedpatterns) or closed features (such as a rectangle or a star). Thefeatures may be considered disconnected because the deposited metal thatdefines the features do not cross or touch neighboring features. Thedepositing of metal in the shape of a disconnected feature, such as astar, may help to increase the bifurcation of the crack. For example,assume that a five-point star is deposited onto the surface of a glasssubstrate. As a crack propagates along the surface of the substrate, itmay intersect the star. The crack may then follow the edges of the star,cracking outward every time it reaches a point in the star, which mayact like a stress concentration point. Accordingly, by changing thenumber of points in the star and the size of the star, the frequency ofthe crack bifurcation may be controlled. Decreasing the size of the staror increasing the number of points in the star may reduce thefragmentation size of the glass substrate.

In some embodiments, metal in the shape of disconnected features may bedeposited onto the surface in order to control the fragmentation shapeof the glass. Shapes like rectangles or stars may be deposited onto theglass surface so that, upon fracturing, the fragments are shaped likethe features, e.g., like a rectangle or star. Controlling the shape ofthe fragmentation may make it easier to separate the fractured glassfrom its environment. For example, chemically strengthened glass may beused in a pipe to hold back the flow of a fluid, such as seawater at awater desalination plant, until the pipe is connected to thedesalination equipment and the plant is ready to being operations. Atthat point, the glass may be intentionally broken (e.g., by increasingthe water pressure in the pipe). The glass may then be filtered out ofthe water, and by controlling the shape of the fragments of glass, itmay be easier or cheaper to filter the majority of the glass out of thewater.

After determining the deposit pattern at operation 702, a mask may becreated according to the deposit pattern at operation 704 and a layer ofmetal may be deposited and patterned on the glass substrate using aphotolithography technique at operation 706. The mask may be createdusing a photoresist and a photomask. For example, a photoresist may bedeposited on top of the layer of metal. Light may be used to shape thephotoresist according to the deposit pattern. After the photoresist hasbeen shaped in accordance with the deposit pattern, the surface may beetched to shape the metal on the glass substrate's surface. Thephotoresist may then be removed.

In some embodiments, the metal layer may be removed from the surface ofthe glass substrate. For example, the layer of metal may serve to impartadditional stresses on the glass surface, changing the stress pattern inthe glass, and afterwards may be removed. As another example, afteradding a metal layer to the glass substrate, the glass may again undergoan ion exchange process, with the layer of metal shielding selectedareas of the glass from the chemically strengthening process. The layerof metal may then be removed, leaving behind a glass substrate with aninhomogeneous stress field caused by the uneven ion exchange at thesurface of the glass substrate.

FIGS. 8A-C illustrate the process of depositing a metal layer 804 on topof a planar sheet of chemically strengthened glass 800 usingphotolithography to control the fragmentation characteristics of theglass, in accordance with embodiments of the present disclosure. Thechemically strengthened glass 800 may be made using any chemicalstrengthening process. For example, the chemically strengthened glass800 may be made using an ion exchange process, such as a K/Na ionexchange process that replaces sodium ions in the surface of the glasswith larger potassium ions when soda lime glass is placed in potassiumnitrate (KNO₃). In some embodiments, the ion exchange process used tostrengthen the glass 800 may involve replacing the sodium ions with someother ions, such as rubidium ions.

As shown in FIG. 8A, a layer of metal 804 may be deposited on a firstsurface of the chemically strengthened glass 800. A mask 802 may beselectively applied on top of the metal layer 804. The mask 802 may beapplied using known photolithography techniques. The layer of metal 804may then be etched as shown in FIG. 8B. The mask 802 may then beremoved, leaving a glass substrate 800 with metal 804 depositedaccording to a deposit pattern on the first surface, as shown in FIG.8C.

FIGS. 9A-B illustrate the process of bonding a patterned glass substrate902 to a chemically strengthened glass substrate 900 to control thefragmentation characteristics of the combined glass substrate, inaccordance with embodiments of the present disclosure. The chemicallystrengthened glass 900 may be made using any chemical strengtheningprocess. For example, the chemically strengthened glass 900 may be madeusing an ion exchange process, such as a K/Na ion exchange process thatreplaces sodium ions in the surface of the chemically strengthened glass900 with larger potassium ions when soda lime glass is placed inpotassium nitrate (KNO₃). In some embodiments, the ion exchange processused to strengthen the glass 900 may involve replacing the sodium ionswith some other larger ions, such as rubidium ions.

The patterned glass substrate 902 may be any type of glass, such asfloat glass, tempered glass, or chemically strengthened glass. Thepatterned glass 902 may be patterned using any technique to control thefragmentation characteristics of the patterned glass, such as thetechniques described in this disclosure. For example, as shown in FIGS.9A and 9B, the patterned glass 902 may be etched to create trenches, andthe trenches may be filled with a metal 904.

The patterned glass 902 may be bonded to the chemically strengthenedglass 900 using any glass bonding technique. For example, the patternedglass 902 may be bonded to the chemically strengthened glass 900 usinglow temperature frit bonding, also known as glass soldering or sealglass bonding. In low temperature frit bonding, the surface of eitherthe patterned glass 902 or the chemically strengthened glass 900 may beheated up. This decreases the viscosity of the heated glass. When theheated glass reaches the wetting temperature, the heated glass is softenough and liquid enough to flow and wet the surface of the other glasssurface. The liquid glass flows into the small imperfections at thesurface of the colder glass, creating a tight seal. When the glass isallowed to cool, it re-solidifies to create a hermetically sealed bondbetween the two glass surfaces.

Alternatively, the glasses 900 and 902 may be bonded using a sodiumsilicate bonding agent, or using anodic bonding (also known as electricfield bonding). For example, a sodium silicate bonding process mayinvolve spinning a 2% sodium silicate solution onto a surface of one ofthe glass substrates at 1500 rpm for 20 seconds to deposit an ultrathin,uniform layer of sodium silicate on the glass surface. The two glasssubstrate may then be brought into contact with each other and manuallytacked together using a hard rod. The substrates may be held togetherwith a force of between, e.g., 10 psi and 3000 psi. The glass substratesmay then be baked as necessary.

As another example, an anodic bonding process may be used to bond thetwo glass substrates together. The surfaces to be bonded together may becleaned with acetone, and the surfaces may be brought in to contact. Avoltage may then be applied across the surfaces to be bound, and theglass substrates may be held together with between 40 psi and 50 psi ofpressure. Heat may also be applied to the glass to increase thetemperature at the bonding site. Other glass-to-glass bonding techniquesas known to one of ordinary skill in the art may also be used.

What is claimed is:
 1. A method of manufacturing a glass substrate tocontrol fragmentation characteristics of the glass substrate, the methodcomprising: determining an etching pattern, the etching pattern beingconfigured to control a fragmentation size of a glass substrate bymodifying a stress field within the glass substrate to create aninhomogeneous stress field; masking a first surface of the glasssubstrate according to the etching pattern, the glass substrate beingchemically strengthened glass, the glass substrate having an exteriorregion and an interior region, wherein the exterior region has residualcompressive stresses and the interior region has residual tensilestresses; etching an unmasked portion of the first surface to produce aplurality of trenches in the first surface; and filling the plurality oftrenches with a filler material to generate the inhomogeneous stressfield in the glass substrate, wherein the filler material is acomposition of a first material and a second material, the compositionhaving a first volume, wherein the composition of the first material andthe second material, when heated, experiences a chemical reaction tocreate one or more products, the one or more products combined having asecond volume, and wherein the second volume is smaller than the firstvolume.
 2. The method of claim 1, wherein a metal filament is insertedinto the composition of the first material and the second material, themethod further comprising: determining that the chemical reaction shouldbe initiated; and running a current through the metal filament, whereinthe current is large enough to cause the metal filament heat up to atemperature sufficient to initiate the chemical reaction between thefirst material and the second material.
 3. The method of claim 1,wherein the composition further includes a third material.
 4. The methodof claim 3, wherein the third material is a catalyst for the chemicalreaction between the first material and the second material.
 5. Themethod of claim 1, wherein the first material is elemental aluminum andthe second material is elemental nickel.
 6. The method of claim 1,wherein the filling the plurality of trenches comprises layering thefirst material and the second material inside the plurality of holes. 7.The method of claim 1, wherein the fragmentation size of the glasssubstrate is less than 250 micrometers, the fragmentation size being anaverage of a width of a plurality of fragments created when the glasssubstrate fractures.
 8. The method of claim 1, the method furthercomprising bonding the glass substrate to a second glass substrate. 9.The method of claim 1, wherein the etching pattern and filler materialare selected to minimize the fragmentation size of the glass substrate.10. The method of claim 1, wherein the etching pattern includes two ormore parallel trenches.
 11. The method of claim 10, wherein thedetermining the etching pattern includes determining an amount of spacebetween each of the two or more parallel trenches.
 12. The method ofclaim 10, wherein the determining the etching pattern includedetermining a width of each of the two or more parallel trenches. 13.The method of claim 3, wherein the third material is an oxide.
 14. Amethod of manufacturing a glass substrate to control fragmentationcharacteristics of the glass substrate, the method comprising:determining an etching pattern, the etching pattern being configured tocontrol a fragmentation size of a glass substrate by modifying a stressfield within the glass substrate to create an inhomogeneous stressfield; masking a first surface of the glass substrate according to theetching pattern, the glass substrate being chemically strengthenedglass, the glass substrate having an exterior region and an interiorregion, wherein the exterior region has residual compressive stressesand the interior region has residual tensile stresses; etching anunmasked portion of the first surface to produce a plurality of trenchesin the first surface; and filling the plurality of trenches with a metalhaving a thermal expansion coefficient greater than the thermalexpansion coefficient of the glass substrate and a Young's modulus thatis greater than the Young's modulus of the glass substrate to generatethe inhomogeneous stress field in the glass substrate by: depositing themetal on the first surface after the first surface has been etched; andpolishing the first surface to remove any metal that is on the firstsurface and not in a trench.
 15. The method of claim 14, wherein thefragmentation size of the glass substrate is less than 250 micrometers,the fragmentation size being an average of a width of a plurality offragments created when the glass substrate fractures.
 16. The method ofclaim 14, the method further comprising bonding the glass substrate to asecond glass substrate.
 17. The method of claim 14, wherein the metal isaluminum.
 18. The method of claim 14, wherein the etching pattern andfiller material are selected to minimize the fragmentation size of theglass substrate.
 19. The method of claim 14, wherein the etching patternincludes one or more disconnected features, the one or more disconnectedfeatures being defined by the plurality of trenches.
 20. The method ofclaim 19, wherein the one or more disconnected features include trenchesin a rectangular configuration.